The overall goal of this proposal is to provide the applicant, Timothy Apodaca, Ph.D., with resources and training to develop into an independent clinical investigator pursuing a research agenda focused on therapeutic mechanisms of action of psychosocial treatments for alcohol problems. This long-term goal will be accomplished by a series of structured training activities, and completion of a mentored study. Training activities of the candidate's career development plan emphasize three goals: (1) developing expert knowledge of therapeutic mechanisms of action for psychosocial treatments of alcohol problems;(2) increasing competency in the theory and conduct of advanced statistical methods;and (3) developing proficiency in therapy process coding, and establishing an independent coding lab for conducting therapy process research. This training will be accomplished at the Brown University Center for Alcohol and Addiction Studies under the mentorship of Dr. Peter Monti, with co-mentorship provided by Dr. Richard Longabaugh and Dr. Christopher Kahler. The proposed research plan will integrate the candidate's newly acquired knowledge in an investigation of hypothesized mechanisms of action of motivational interviewing (Ml) in the context of a randomized, controlled trial of Ml conducted in a hospital trauma center. While evidence supports the efficacy of Ml for substance use disorders, little is known about how Ml works. The proposed study will utilize process coding to investigate the impact of including a significant other in Ml sessions compared with individual sessions. In addition, the study will seek to replicate and extend other research on the role of therapist behavior and specific types of patient speech on future behavioral outcomes. The long-term goal of this line of research is to identify aspects of patient, therapist, and significant other speech and behavior in Ml sessions that contribute to reductions in drinking and associated negative consequences. Identifying the active ingredients of motivational interviewing can inform future training efforts in the dissemination of this alcohol treatment.